There has been much development of organic compounds as semiconductor materials. In particular, high performance unipolar p-type and n-type polymer semiconductors have been developed in recent years, having hole and electron mobility, respectively, approaching 1 cm2/V·s. Polymer semiconductors with high transport mobility in thin film transistors are useful in many applications, including displays and RFIDs.
Ambipolar organic thin film transistors capable of conducting both holes and electrons in p- and n-channel region operations have drawn recent attention. Such devices can provide an alternative approach for construction of complementary digital integrated circuits which mimic the prevailing complementary metal-oxide semiconductor (CMOS) technology. Such CMOS-like digital circuits have many advantages such as greater speed, higher noise immunity, lower power dissipation, and better tolerance of variability and shifts in transistor operating characteristics as compared to non-complementary circuits.
Ambipolar transistors can be fabricated by using (i) two stacked layers of discrete p- and n-channel semiconducting materials; (ii) one two-component layer comprising a blend of unipolar p- and n-type organic semiconductors; or (iii) one layer of a single-component material with either symmetric or asymmetric electrodes.
However, the use of unipolar p-type and n-type organic semiconductors for bilayered (i) or mixed layered (ii) ambipolar OTFTs requires complicated fabrication procedures or such devices have shown poor performance. For design (iii), although many of the current organic semiconductor materials show ambipolar charge transport properties, such materials require strict operating conditions (e.g., high vacuum), special dielectric materials, or very low work function electrode materials.
Ambipolar semiconductor materials with balanced high hole and electron mobilities could greatly simplify device fabrication, especially when using a solution processing technique such as ink-jet printing for complex fabrication of logic circuits. Currently, there are very few single-component semiconducting materials that demonstrate stable ambipolar operation characteristics in an OTFT. Known ambipolar single-component semiconductor materials typically demonstrate low and unbalanced hole and electron mobilities (10−5-0.1 cm2/V·s).
Very recently, an ambipolar polymer with hole mobility of 0.003 cm2/v·s and electron mobility of 0.04 cm2/V·s was described in Kim et al., Adv. Mater. 2010, 22, 478-482.
Accordingly, there is a need for production of alternative ambipolar organic materials useful for production of efficient electronic devices.